1. Field of the Invention
The present invention relates to a system for acquiring, displaying and archiving digital time sampled signals, and more particularly, for a system which acquires, displays and archives data from a large number of sensors.
2. Description of Related Art
There exist many systems which consist of arrays of transducers, or sensors, which are arranged in a complex spatial arrangement and for which digitized representations of the signals has to be acquired, monitored and ultimately archived for later use. Acquisition is the process of moving the sampled, digitized data from a sensor onto some type of temporary storage device. Monitoring is the process of viewing a representation of the data and possibly verifying that the data is of good quality. Archiving is the process of storing the acquired data onto a permanent (usually removeable) medium like magnetic disk or tape or optical disks.
Common examples of such systems include vibration testing systems having arrays of accelerometers, temperature mapping systems having arrays of thermocouples and medical instruments such as electrocardiographic body surface potential measurement system. Another medical system is a magnetic source imaging system which uses a complex arrangement of hundreds of superconducting coils arranged over the chest of patient, known as magnetocardiography, or over the head of a patient known as magnetoencephalography. In these systems, it is necessary to perform the three functions of acquisition, monitoring and archiving.
Typically each sensor produces an analog, time-varying signal. These are usually digitized and stored on an archive device. Since there are many sensors in these systems, data rates for acquisition in real-time exceed the data rate of archive devices. The use of faster archive devices becomes increasingly more expensive, and a limiting factor for real-time archiving.
When hundreds, or thousands, of sensors are involved, it becomes very difficult to select or to jointly view the signal from selected sensors. Usually some method is provided to choose signals for display by, for example, entering channel numbers, each related to a specific sensor, or a group of sensors. Typically, a few dozen waveforms are arranged one above the other. These may be viewed on a stripchart or stripchart-like device. These devices produce waveforms on paper that create a plot of a given signal value versus time. The paper continuously runs through the recorder showing the signals as they vary over time. Typically, the individual traces are assigned differing colors.
Another device which may be used to display the selected signals is a cathode ray tube (CRT) display. On a CRT display, the usual solution involves a scrolling-type display, in which the waveforms appear to enter from one side of the display window, slide sideways through the window at a constant rate and then disappear out the side opposite to which they entered.
This fixed arrangement of traces on the stripchart or CRT display does not allow the viewer or operator of the system to appreciate the inter-relation of signals caused by the physical placement of sensors. In order to understand, or further process the acquired data, one must appreciate the relative positioning of the sensors which are producing the signals being monitored.
Another problem involves interaction between the system operator and the viewing/acquisition system. Typically, the operator must be able to move around the piece of equipment under test or around the patient in a medical system. With standard operator input devices, the operator has to continually return to the display console to adjust the system parameters or the display parameters.
Thus, there is a need to acquire data, temporarily store the acquired data, display the data and archive the data in such a way that the acquisition of new data is not impeded.